metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: Gray, tan, or white with reddish tint; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline masses); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- Gray, tan, or white with reddish tint
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Gray, tan, or white with reddish tint; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline masses); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed through the regional metamorphism of quartz sandstone. Under high heat and pressure, quartz grains recrystallize and fuse together. It can range in age from Precambrian to more recent geological eras.
Uses & applications
Used widely as crushed stone for road construction and railway ballast. Also used as a decorative building stone, in countertops, and as a source of silica in glass manufacturing.
Geological facts
Quartzite is so tough that it often survives the weathering process much longer than surrounding rocks, forming prominent ridges and hills. It is often harder and more durable than granite.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by steel) and its grainy, sandpaper-like texture that lacks the foliated layers of gneiss. It is commonly found in mountainous regions worldwide.
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